The M10 motorway is closed in both directions between junction 1 and junction 7 as well as some arterial roads in Hemel Hempstead.

Motorists have been told not to go "anywhere near the M1 from the M25 upwards".

Hertfordshire police said about 70 schools in the Hemel Hempstead and St Albans areas would also be closed on Monday.

At Heathrow airport some flights were forced to delay landing because of smoke, but Luton airport was operating as usual.

The Buncefield depot is a major distribution terminal operated by Total and part-owned by Texaco, storing oil, petrol as well as kerosene which supplies airports across the region, including Heathrow and Luton.

The country's fifth largest fuel distribution depot, it is also used by BP, Shell and British Pipeline.

Police said there was no indication the explosion would cause fuel shortages and warned against panic-buying.

A spokesman for Total said: "We are doing everything we can to support the emergency services and to bring the situation under control."

A spokesman for the Department for Trade and Industry said it was too early to say what the effect would be on fuel supply but oil companies were getting oil from other parts of the south east and across the UK.

A spokesman for the Health and Safety Executive said it would be investigating the incident.

Concerned relatives can call a police casualty bureau on 0800 096 0095, or from abroad on 0207 1580125.

BUNCEFIELD FUEL DEPOT BLASTS

With light winds blowing to the south-east and south-west, smoke is likely to be spread over large parts of southern England by Monday